3-54 BOP HIPWR 111315All non-control characters are sent via the serial port of the command originator. The controlcharacter BS is echoed as BS Space BS. Only the first control character is returned in responseto either a CR LF or LF CR character sequence (see Figure 3-17).3.5.6.2.1 XON XOFF METHODThe XON XOFF method allows the BOP to control when the command originator is allowed tosend data. The command originator can only send data after the XON (transmission on) charac-ter (011 H) has been received; the command originator stops sending data after receiving theXOFF (transmission off) character (013H), and waits until the XON character is received beforesending additional data.Control characters, either CR or LF, are returned as XOFF CR if echo mode is on, and as XOFFif echo mode is off. XOFF stops data from the command originator and the BOP returns the nor-mal sequence of CR LF (if echo mode is enabled).3.5.6.2.2 ECHO MODEEcho mode is one method of ensuring data is transferred without errors. This mode should onlybe enabled when errors in operation are detected.Each byte (character) is echoed back to the sender where it is verified as the same characterthat was just sent. If the wrong character is echoed back, sending the ESC character clears theline to allow retransmission of the character. It is important the CR and LF characters are NOTsent until the verification process is complete.When working in echo mode, it is possible to receive the NAK (15 hex) from the BOP. This indi-cates an unknown quantity of echoed characters have been lost due to a queue overflow prob-lem. The error queue will also contain the -400, QUE error message, To prevent this, pleaseinsure the received data string does not exceed 127 characters between line terminators and nomore than four queries are sent between line terminators in SCPI mode of operationAll non-control characters are sent via the serial port of the command originator.3.5.6.2.3 PROMPT METHODThe command originator sends a message line (command) to the BOP and waits until theprompt sequence CR LF > (3E H, 6210 ) is received. The BOP sends the prompt sequenceCR LF > to the command originator indicating the power supply is ready to receive the nextcommand and data will not be lost. This method is useful in an interactive mode as well as withcertain process controllers.3.5.6.3 USING SCPI COMMANDS FOR RS 232 COMMUNICATION.The unit must be in remote mode before the RS 232 commands to affect the output can be exe-cuted (e.g., VOLT 10;OUTP ON). This can be accomplished by sending SYST:REM ON prior tosending any commands that affect the power supply output. (See PAR. B.142 and Figure B-11)3.5.6.4 ISOLATING RS 232 COMMUNICATION PROBLEMSA Loop Back test can be run from the front panel to aid in isolating RS 232 communication prob-lems. The unit is designed to pass the test only with the Loop Back test connector (part of Kit219-0436, see Table 1-4) installed.
